PEOCEEDINGS OF UNITED STATES NATIONAL MUSEUM. -309 



'No. 1 of the small thermometers and Negretti & Zambra's Xos. 43230 

 (between 70° and 80°), 38982, 40007, 426G6, and 43227 (between 70^ and 

 90°), are the only ones to which it is worth while to apply a correction 

 in practice. The other differences, being less than half a degree, may 

 be disregarded as not likely to exceed the ordinary eiTors of observation. 



Table A. — Tliermomeler corrections. 



There are some practical difficulties in the use of these delicate instru- 

 ments, which it is well to mention. 



1. The bulbs are long and large compared to the diameter of the 

 column of mercury. Hence the latter is very sensitive and responds 

 quickly to the heat of the hand, even through the walls of the heart, or, 

 in small fishes, of the abdomen. Thus in a small living blue-fish {Poma- 

 tonuis saltatrix (Linn.), Gill), observed September 8, in an aquarium- 

 tank, the water being at 07^ F., a thermometer passed into the stomach 

 by way of the gullet showed G8.8° ; but, holding the fish in my left 

 hand, I observed that the mercury was slowly rising and had reached 

 73° in two minutes. This accession of heat was communicated through 

 the thin walls of the abdomen from my hand. 



2. Owing to the extreme fineness of the mercurial column it is quite 

 difficult to distinguish it at all from the empty part of the tube, unless 

 the light falls upon it at exactly the proper angle. When taking the 

 temperature of a struggling fish on the deck of a vessel, in the full 

 glare of the sun, and with the thermometer perhaps smeared with blood, 

 it is impossible to be too careful in guarding against errors of observa- 

 tions. 



3. A difference of several tenths may be apparent in the reading 

 according to the i)Osition of the observer. Looking down upon the 

 column he reads too low ; looking up, too high. His eye should be exactly 

 opposite the toi) of the mercurial column. After use, the thermometer 

 should be wiped perfectly clean and laid back in its i>roper bed in the 

 case, lest in the hurry of the next observation the wrong one be taken 

 up, and time lost. 



